1. Field of the Invention
This invention relates to a process and apparatus for the production of a lithographic printing plate free from printing stains at end parts.
2. Description of the Prior Art
PS plates using light-sensitive agents of positive type, comprising, as predominant components, diazo compounds and phenol resins, or light-sensitive agents of negative type, comprising, as predominant components, acrylic monomers or prepolymers have been put to practical use as a lithographic offset printing plate, but subjected to plate making by contact exposure of a previously image-recorded film precursor because of the low sensitivity thereof.
On the other hand, a copy input, correction, edition, layout and paging, from first to last, have lately been computer-operated with progress of the computer image processing, the storage of large capacity data and the data communication technique, and an electronic edition system has been put to practical use in which an output is promptly attained in a terminal plotter in a remote place by a high speed communication network or satellite communication.
In particular, an electronic edition system is highly required in the field of newspaper printing needing promptness. In the field of subjecting an original copy to storage in the form of a film and as occasion demands, reproducing a printing plate, too, it is considered at the present time that with progress of large capacity recording media such as optical disks, an original is stored as digital data in these recording media.
However, a printing plate of such a direct type that a printing plate is directly prepared from an output of a terminal plotter has hardly been used and the fact is that even where an electronic edition system is operated, an output is effected on a photographic film of silver salt, which is then subjected to contact exposure on a PS plate to prepare a printing plate. One reason therefor is that it is very difficult to develop a printing plate of direct type having such a high sensitivity as capable of preparing a printing plate in a practical period of time by a light source of output plotter (e.g. He-Ne laser, semiconductor laser, etc.).
An electrophotographic light-sensitive material has been taken into consideration as a light-sensitive material having such an optical sensitivity as capable of providing a printing plate of direct type. Preparation of a printing plate by electrophotography has already been known as a method comprising forming a toner image and removing a photoconductive layer on a non-image area. For example, electrophotographic lithographic printing plates are described in Japanese Patent Publication Nos. 17162/1962, 6961/1963, 7758/1963, 2426/1966, 39405/1971, 19509/1975, 19510/1975, 2437/1977, 145538/1979, 134632/1979, 105254/1980, 153948/1980, 161250/1980, 147656/1982, 161863/1982, etc.
In the above described methods, using a resin capable of being dissolved or swelled in an alkaline solvent and released as a binder resin of an electrophotographic light-sensitive material, a toner image is held as a resist and another area than the toner image is removed to expose a hydrophilic area and obtain a lithographic printing plate.
In the case of printing on a rolled paper by a rotary press machine, as in newspaper printing, using the above described offset printing plate, however, printing stains occur on positions corresponding to the end parts of the printing plate.
As a method of preventing end parts from contamination by a lithographic printing plate coated with a photopolymer, it has been proposed to bevel the end parts of tile lithographic printing plate in Japanese Patent Publication No. 46754/1982. According to this method, however, the problem of the printing stains cannot sufficiently be solved.
In an electrophotographic lithographic printing plate prepared by a process comprising at least statically charging, exposing, developing with a toner, fixing the toner and removing another photoconductive layer than the toner image, the toner adheres to end parts during the toner development to cause printing stains and in the case of reversal development, in particular, the printing stains are remarkable. As a method of preventing such terminal stains, it has been proposed to provide the end parts (side surfaces) of an electrophotographic lithographic printing plate with an insulating resin layer (Japanese Patent Laid-Open Publication No. 178240/1988). That is, it is considered that as one cause of printing stains by a lithographic printing plate obtained by reversal development of an electrophotographic lithographic printing plate, a toner adheres to the end parts of the electrophotographic lithographic printing plate, too, during the reversal development and an ink adheres to these parts during printing, resulting in printing stains. Based on this consideration, an insulating resin is coated onto tile end parts of an electrophotographic lithographic printing plate, whereby the adhesion of the toner, during the reversal development, is prevented. Provision of the end parts with a layer of resin having a higher solubility in an alkaline solution than a resin in a light-sensitive layer has been proposed as described in Japanese Patent Laid-Open Publication Nos. 61654/1990 and 66566/1990, but the problem of staining cannot be solved by this proposal.
In Japanese Patent Laid-Open Publication Nos. 261660/1989, it has been proposed to provide a means for removing a toiler adhered to between a developing section and fixing section, but the toner not still fixed is partly retained and printing staining cannot sufficiently be resolved.